The invention concerns devices and methods for the determination of at least one variable associated with the electromagnetic radiation from an object under test.
In order to determine the radiation diagram of and object under test, it has already been proposed that use should be made of devices that come in the form of a network of probes distributed in an arc around the object under test to be studied (a circular network).
We are familiar in particular with devices of this type that include means which allow the arc of probes and the object under test to rotate in relation to each other around an axis that corresponds to the diameter of the arc. In general, it is the object under test which rotates on itself around a vertical axis which corresponds to the diameter of the arc, but it can be envisaged, in a variant, that it is the arc of probes that rotates on itself, while the object under test remains fixed.
In this way, the network of probes measures the radiation of the object under test in successive planes spread around the axis of rotation of the arc and the object under test. In general then, the measurements are therefore taken on a sphere that totally surrounds the object under test.
We are also familiar with the use of networks of probes in an arc by moving, in a relative manner, the object under test perpendicularly in relation to the plane of the network of probes so as to measure the radiation on a cylinder enclosing the object.
The arrangement of a network of probes in a arc, whether used for measurements in spherical coordinates or measurements in cylindrical coordinates, nevertheless have limitations associated with the discrete measurement pitch imposed by the arrangement of the probes in a network.
In contrast to the case of a single probe which can be moved continuously, the use of a network of probes imposes constraints on the dimensions of the object under test, and whose field is to be measured.
In particular, according to theories that are well known in the near-field area, the number of sampling points is linked to the electrical dimension of the object under test.
Reference can be made in this regard to:
Hansen, J. E., Editor (1988) Spherical Near-Field Antenna Measurements, London: Peregrines 
In particular, the number of sampling points is a function of the radius (R) of the minimum sphere or of the minimum cylinder surrounding the object under test and verifies:N≈(2πR/λ)+n where n≈10
As a consequence, it is understood that a network of N probes allows only the analysis of objects contained in a sphere or in a cylinder with a maximum radius R.
In other words, for a given analysis frequency or wavelength, and for a given network of probes, there exists a maximum size of objects capable of being analysed.